Moisture-curable compositions, based on alkoxysilyl-containing polymers, are known. Such polymers undergo hydrolysis and condensation on contact with moisture, typically in the presence of a cure catalyst. Suitable known catalysts for curing alkoxysilyl-containing polymers include organometallic compounds containing metals such as tin, titanium, zirconium, zinc and bismuth. Organotin compounds such as, e.g., dibutyltin dilaurate (DBTDL) are widely used as catalysts to accelerate the curing of a number of different alkoxysilyl-containing silicone and non-silicone resins and moisture-curable compositions such as coatings, sealants and adhesives formulated with such resins. Environmental regulatory agencies and directives, however, have increased, or are expected to increase, restrictions on the use of organotin compounds in formulated products. While formulations containing greater than 0.5 weight percent DBTDL currently require labeling as toxic under a reproductive 1B classification, DBTDL-containing formulations are proposed to be completely phased out in consumer applications within the next few years.
Other organotin compounds such as dioctyltin and dimethyltin may be given a temporary reprieve from regulation but will likely be regulated in the near future. It would therefore be beneficial to provide non-tin metal catalysts for the curing of alkoxysilyl-containing polymers of both the silicone and non-silicone types.
Desirably, substitutes for organotin curing catalysts should exhibit performance profiles that are about as good as, if not better than, those of organotin compounds in terms of curing rate, storage stability and properties of the cured compositions. There have been many proposals for the replacement of organotin compounds by other organometallic compounds. Each of the proposed tin substitutes has its particular advantages and disadvantages compared with known organotin cure catalysts. Therefore, there remains a need to overcome deficiencies of known organometallic cure catalysts for the curing of alkoxysilyl-containing polymers.